It is known that the incorporation of solid inorganic fillers into solid olefin polymers increases their rigidity. For example, polyethylene compositions containing finely divided silica, glass fiber, talc, asbestos, calcium carbonate or the like are stiffer than the base polyethylene resin. But such filled compositions are also known to be more brittle, have lower impact strength, lower tensile strength and are less tough.
Numerous proposals have been suggested in the art to avoid such deleterious effects of filler addition, generally by particularly selecting and specifying the plastic component or the filler component or both, or by particularly treating the filler or the starting plastic or the filled composition.
For example, in Japanese Patent Publication No. 7894/1972 (published Mar. 6, 1972 from Application No. 69212/1967 filed Oct. 29, 1967), Aishima et al. compound thermoplastic olefinic polymers with inorganic fillers which are oxides, hydroxides or carbonates in the presence of monomeric acrylic acid or methacrylic acid, or their metal salts, or mixtures of such metal salts and a vinylic monomer containing an ester group. In U.S. Pat. No. 3,694,403, Aishima et al. in a related development describe using certain specified magnesium carbonates as filler with an unsaturated carboxylic acid as optional component improving impact resistance.
In U.S. Pat. No. 3,802,913, MacKenzie describes a curable composition comprising an ethylene polymer, a curing agent and a filler that is treated with an organosilane, e.g., vinyl silane.
In British Specification 1,195,214 published June 17, 1970, Bixler and Fallick describe reinforcing fillers for organic polymer compositions prepared by compounding a non-reinforcing filler with (a) an ethylenically unsaturated organic compound having chemical affinity for the surface of such filler, (b) an organic compound having at least two polymerizable ethylenic linkages in the molecule and (c) a free-radical generator, in specified proportions. Organic polymer compositions of such treated fillers are said to be characterized by increased toughness. In U.S. Pat. No. 3,272,772, Russell describes improved fillers for chlorinated high density polyethylene wherein the fillers are treated with polymerizable polar vinyl monomers which are monoethylenically unsaturated.
However, despite these and other disclosures of the prior art, it would still be desirable to provide highly filled thermoplastic compositions with improved properties, especially compositions of polyethylene, e.g., high density polyethylene, and like olefin polymers, having improved toughness. Accordingly, it is an object of this invention to provide such improved compositions and method and means to obtain the same. Other objects and advantages of this invention will become evident in the description that follows.